Wow.

Sold from a Smoking Brim-Full of Bullets(19 Keys) and a Strange Pro KS Cow Mangler 5000(~2 Keys)(21 Keys total)

http://backpack.tf/profiles/76561198128764134#!/compare/1459382400/1459555200

http://backpack.tf/profiles/76561198053143446#!/compare/1458370800/1459555200

Sold for a Disco Beat Down Bone Dome(20 Keys) and ~1 Key in Sweets(21 Keys total)

http://backpack.tf/profiles/76561198158008994#!/compare/1456560000/1456905600

Seller at 17 Keys

http://www.tf2outpost.com/trade/28152212

With the seller at 17 and two sales at 21, 17-21 Keys should be fine.

Additional Proof/Counter-Proof/Constructive Criticism/Feedback is always appreciated.